1. Field of the Invention
The present invention relates to a communication terminal apparatus, and more particularly to a communication terminal apparatus for use in a communication system in which at least one line having a plurality of channels is used by a plurality of communication apparatuses.
2. Description of the Prior Art
Conventionally, an ISDN (integrated services digital network) system is known as a communication system of this type. For instance, in a basic interface of a user network of this ISDN line, one line is provided with three communication channels comprising two information channels (B channels) and one control channel (D channel), and a maximum of eight terminals are connected to this line. When a communication line is not in use, it is possible to effect communication in response to a request for communication from each terminal.
When a small number of lines are utilized by a plurality of terminals as in the case of the ISDN system, even if one terminal attempts communication, it is impossible to communicate when all the information channels are busy. At that time, there is a drawback in that it is impossible for the user to know whether or not communication is possible unless a request for communication is actually made on each such occasion.